Thermoresponsive super water absorbent hydrogels prepared by frontal polymerization

Frontal polymerization was used as an alternative technique for the preparation of super water absorbent hydrogels obtained from acrylamide and 3‐sulfopropyl acrylate, potassium salt (SPAK) in the presence of N,N′‐methylene‐bisacrylamide as a crosslinker. All samples were synthesized in dimethyl sulfoxide, and their swelling behavior in water was investigated. It was found that their features are dependent on the monomer ratio used, which influenced the porous morphology, and consequently, the swelling capability. The swelling ratio ranges from about 1000% for the acrylamide homopolymer up to 14,000% for the sample containing 87.5 mol % of SPAK, thus indicating that this parameter can be easily tuned by using the appropriate monomer ratio. The affinity towards water was eventually confirmed by contact angle analysis. Polymer hydrogels made from at least 62.5 mol % SPAK exhibit a thermoresponsive behavior, with a lower critical solution temperature of ～30 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2486–2490, 2010     

Structure and shear orientation of a side chain liquid crystal polymer studied by small angle X-ray scattering

We have studied the structure and shear flow behaviour of a side chain liquid crystal polymer, namely P₁₂, in the smectic (SmA_d) phase. Simultaneous oscillatory shear and small angle X-ray scattering experiments showed that, as expected, the shearing of P₁₂ at high frequency and large strain amplitudes leads to the alignment of the smectic layer normals parallel to the neutral direction. It was also found that, on erasing the memory of the prior shear alignment through melting, P₁₂ can unexpectedly orient with the smectic layers perpendicular to the shear flow direction (b-configuration). We speculate that the b-configuration is adopted due to a counter-balance between the rather long spacer in P₁₂ which decouples mesogens from the backbone, and the oscillatory character of the shear applied to P₁₂.     

Inner solvers for interior point methods for large scale nonlinear programming

This paper deals with the solution of nonlinear programming problems arising from elliptic control problems by an interior point scheme. At each step of the scheme, we have to solve a large scale symmetric and indefinite system; inner iterative solvers, with an adaptive stopping rule, can be used in order to avoid unnecessary inner iterations, especially when the current outer iterate is far from the solution. In this work, we analyse the method of multipliers and the preconditioned conjugate gradient method as inner solvers for interior point schemes. We discuss the convergence of the whole approach, the implementation details and report the results of numerical experimentation on a set of large scale test problems arising from the discretization of elliptic control problems. A comparison with other interior point codes is also reported. This research was supported by the Italian Ministry for Education, University and Research (MIUR) projects: FIRB Project: “Parallel Nonlinear Numerical Optimization PN ² O” (grant n. RBAU01JYPN, ) and COFIN/PRIN04 Project “Numerical Methods and Mathematical Software for Applications” (grant n. 2004012559, ).     

On the solution of indefinite systems arising in nonlinear programming problems

This work is concerned with the convergence properties and the numerical analysis of the preconditioned conjugate gradient (PCG) method applied to the solution of indefinite linear systems arising in nonlinear optimization. Our approach is based on the choice of quasidefinite preconditioners and of a suitable factorization routine. Some theoretical and numerical results about these preconditioners are obtained. Furthermore, we show the behaviour of the PCG method for different formulations of the indefinite system and we compare the effectiveness of the proposed variants. Copyright © 2007 John Wiley & Sons, Ltd.     

In‐line coupled single drop liquid–liquid–liquid microextraction with capillary electrophoresis for determining fluoroquinolones in water samples

A simple in‐line single drop liquid–liquid–liquid microextraction (SD‐LLLME) coupled with CE for the determination of two fluoroquinolones was developed. The method is capable to quantify trace amount of analytes in water samples and to improve the sensitivity of CE detection. For the SD‐LLLME, a thin layer of organic phase was used to separate a drop of 0.1 M NaOH hanging at the inlet of the capillary from the aqueous donor phase. By this way, the analytes were extracted to the acceptor phase through the organic layer based on their acidic/basic dissociation equilibrium. The drop was immersed into the organic phase during 10 min for extraction and then it is directly injected into the capillary for the analysis. Parameters such as type and volume of organic solvent phase, aqueous donor, and acceptor phases and extraction time and temperature were optimized. The enrichment factor was calculated, resulting 40‐fold for enrofloxacin (ENR) and sixfold for ciprofloxacin (CIP). The linear range were 20–400 μg/L for ENR and 60–400 μg/L for CIP. The detection limits were 10.1 μg/L and 55.3 μg/L for ENR and CIP, respectively, and a good reproducibility was obtained (4.4% for ENR and 5.6% for CIP). Two real water samples were analysed applying the new method and the obtained results presented satisfactory recovery percentages (90–100.3%).     

The formation of non-soluble complexes between polyethyleneimine-anions and their potential use to isolate enzymes

The aqueous solution behavior of polyethyleneimine (a synthetic cationic polymer) in the presence of anions with two or more electrical charges (citrate, phosphate, sulphate, malate, malonate and succinate) was studied by means of turbidimetry and light scattering. Polyethyleneimine forms non-soluble complexes with these anions, which behave as a pseudo-polyampholyte with an isoelectrical pH value dependent on the type of anion. The effect of pH, polymer concentration and ionic strength on the non-soluble complexes formation was examined. The complex precipitation pH range was between 3.5 and 8.0 and also depended on the type of anion. The complex formation was inhibited by the ionic strength in agreement with the electrostatic mechanism of the non-soluble complex formation. Model proteins with isoelectric pH from 1 to 10 were assayed in orden to be precipitated by these complexes. It was found that the non-soluble polyethyleneimine-anion complexes have the property to precipitate macromolecules charged with an opposite electrical charge.     

Influence of synthesis conditions on the cross-link architecture of silsesquioxanes prepared by in situ water production route

The esterification reaction between carboxylic acids and alcohols has been used as the source of water for the hydrolysis-condensation reactions of difunctional and trifunctional organosilanes. Diphenylsilanediol (DPDO) has been reacted with methacryloxypropyltrimethoxysilane (MPTMS) and glycidoxypropyltrimethoxysilane (GPTMS) and the obtained products have been characterized by vibrational spectroscopy (FT-IR, FT-Raman) nuclear magnetic resonance (NMR) and gel permeation chromatography. The relation between water availability from the in situ water production process (ISWP) and silsesquioxanes morphology has been evaluated in the case of DPDO/MPTMS mixtures, changing molecular features of acids and alcohols. These measurements have shown that the pK of the carboxylic acid used in the esterification reaction has a valuable influence on the silanes cross-linking ability. Acids with low pK values and heteroatoms substituents favor the silane hydrolysis and allow the growth of high molecular weight species. Using acetic acid/ethanol mixture leads to the best results for DPDO/MPTMS reaction, with a narrow distribution of silsesquioxane species. Under the same conditions, the reaction of DPDO with GPTMS produces polymeric species and only avoiding the presence of the difunctional precursor allows to limiting the silsesquioxanes species growth.